1. Field of Invention
Embodiments generally relate to a semiconductor device, a capacitor, and to a non-volatile memory device including nanodots and a capacitor.
2. Related Art
A non-volatile memory device can retain data stored therein even in the absence of a power supply. The non-volatile memory device, according to data storage methods, may be divided into a charge storage type and a charge trap type.
A floating gate type non-volatile memory device includes memory cells that comprise a tunnel insulating layer, a floating gate, a charge blocking layer and a control gate electrode stacked sequentially on a substrate. The floating gate type non-volatile memory is configured to store data by storing charges in a conduction band of the floating gate.
A charge trap type non-volatile memory device includes memory cells that comprise a tunnel insulating layer, a charge trap layer, a charge blocking layer, and a gate electrode stacked sequentially on a substrate. The charge trap type non-volatile memory device is configured to store data by trapping charges in deep level trap sites inside the charge trap layer.
A charge trap type non-volatile memory device is more appropriate for manufacturing a highly integrated memory device because it has little interference between neighboring memory cells, in comparison with a charge storage type non-volatile memory device. However, as for the above-described charge trap non-volatile memory device, trap sites are concentrated at the interface between the charge trap layer and the charge blocking layer, and the interface is unstable, which may cause an unstable program/erase operation of the memory device and charge loss. In particular, during an erase operation, charges may be introduced into the charge trap layer from the control gate through the charge blocking layer, which may cause a reduction in erase speed.
To overcome these disadvantages, a non-volatile memory device that stores charges by using nanodots has been developed. However, data retention characteristics of a non-volatile memory device that includes nanodots may be deteriorated as charges are drained off to the nanodots with a reduction in cell area caused by a higher integration degree of a semiconductor device. In addition, a range of threshold voltage variations of the memory cells may not be wide enough during an erase operation.
Meanwhile, a capacitor used in a semiconductor device comprises a lower electrode, a dielectric layer, and an upper electrode stacked on and upon another in a sequential manner and functions to store charges. However, a higher integration degree of a semiconductor device may cause a reduction in cell area. As a result, capacitance of the capacitor may be reduced, and charges stored in the capacitor may be drained off.